alkenes and polymers

Question 1

which is stronger pi or sigma bond and why

Answer 1

sigma
between 2 nuclei

Question 2

trans / E

Answer 2

opposite sides

Question 3

cis / Z

Answer 3

same side

Question 4

define electrophile

Answer 4

an electron deficient species with a vacant orbital often positively charged

Question 5

define addition reaction

Answer 5

where one or more groups are added on to a molecule to give a single product

Question 6

how can the stability of the carbocation intermediate be increased

Answer 6

methyl groups are weakly electro donating (compared to H) so the stability increases as the number of methyl groups attached to C+ increases

Question 7

test for unsaturation/alkene

Answer 7

bromine water + ethene/propene
shake together/bubble gas through
orange bromine water decolourised

Question 8

what is required for polymerisation

Answer 8

any short chain alkene
high pressure
peroxide initiator that produces free radicals

Question 9

hydration of an alkene

Answer 9

steam + conc phosphoric acid
makes an alcohol

Question 10

another test for an alkene

Answer 10

acidified potassium manganate
purple—> colourless
makes a DIol

Question 11

hydrogenation of an alkene

Answer 11

use heat (above 150°) + nickel catalyst
add hydrogen

(forms an alkane)

Question 12

order of stability of carbocations

Answer 12

primary<secondary<tertiary

Question 13

which will be the main route of an asymmetrical electrophilic addition reaction

Answer 13

the more stable one
so secondary over primary
tertiary over secondary

Question 14

4 features of a pi bond

Answer 14

2 areas of overlap (above and below nuclei)
parallel overlap
weaker than sigma
between 2 p orbitals

Question 15

4 features of a sigma bond

Answer 15

single area of overlap (between 2 nuclei)
horizontal overlap
stronger than pi
between 2 p orbitals

Question 16

define heterolytic bond fission

Answer 16

covalent bond between 2 species broken in an unequal manner
results in the bond pair of electrons being retained by one of the chemical species
the other does not retain any
one +ve charge product (an electrophile), one -ve charge

Question 17

define homolytic bond fission

Answer 17

dissociation of a molecule where one electron is retained by each of the original fragments of the molecule.
two free radicals are obtained
as each chemical species retains one electron from the bond pair

Question 18

define geometric isomerism

Answer 18

due to there being no free rotation about a C=C double bond (or in a ring structure) there are 2 different groups on each of the double bonded carbon atoms.

Question 19

what properties do geometric isomers display

Answer 19

different physical properties
same chemical properties

Question 20

how to decide if a compound is cis Z or trans E when it has all different groups attached

Answer 20

the atom with the highest atomic number takes priority

Question 21

combustion of alkene/alkane method

Answer 21

burn one drop on a tuft of mineral wool on a heatproof matt

Question 22

comparison of results for combustion of alkene/alkane

Answer 22

alkane- yellow luminous flame

alkene- sooty yellow luminous flame (incomplete combustion)

Question 23

method of bromine water with alkene/alkane

Answer 23

1cm3 of bromine water in a test tube
add 3 drops of ane/ene
mix

Question 24

comparison of results for alkene/alkane with bromine water

Answer 24

alkane- orange layer on top lower layer colourless (no reaction)

alkene- orange bromine water decolourised. upper layer of bromoalcohol

Question 25

method of potassium manganate and dilute H2SO4 with alkene/alkane

Answer 25

2 drops KMnO4
1cm3 dilute H2SO4
few drops of ene/ane
shake at room temp

Question 26

comparison of results for KMnO4 and H2SO4 for alkene/alkane

Answer 26

alkane- no change (no reaction)
alkane floats on top

alkene- pink->brown->colourless
alkene floats on top

Question 27

method stability in water alkene/alkane

Answer 27

1cm3 distilled water
few drops of ene/ane
shake

Question 28

comparison of results solubility in water alkene/alkane

Answer 28

alkane- 2 layers formed after shaking
organic layer on surface

alkene- 2 layers formal after shaking
organic layer on surface

Question 29

cracking produces alkenes method

Answer 29

• 2-3cm3 medicicinal parafin onto mineral wool in a boiling tube
• set up apparatus
• Al2O3 is a catalyst
• heat catalyst (not mineral wool) continuously until bubbles appear
• discard first test tube (just hot air) then collect several tubes of gas
• remove delivery tube from water before cooling (to avoid suckback)

Question 30

combustion test for alkene gas (after cracking)

Answer 30

hold test tube upside down + hold a flame to the mouth
produces a slight puff

Question 31

apparatus for cracking

Answer 31

test tube with mineral wool + medicinal parafin and Al2O3 catalyst
delivery tube from this test tube into water trough
place test tube to collect gas into the water trough, over the delivery tube

Question 32

alkene to bromoalcohol

Answer 32

aqueous Br2

Question 33

alkene to alcohol

Answer 33

H2O gas (steam)
conc H3PO4

Question 34

alkene to bromoalkane

Answer 34

HBr

Question 35

alkene to dibromoalkane

Answer 35

Br2

Question 36

alkene to diol

Answer 36

KMnO4
dilute H2SO4
purple -> colourless

Question 37

alkene to alkane
(hydrogenation)

Answer 37

H2
Ni catalyst
150 degrees C

Question 38

3 ways to reduce plastic waste

Answer 38

recycle
incinerate
chemical feedstock

Question 39

how does recycling work

Answer 39

waste chopped into small peices
melted + moulded

Question 40

how does incineration work

Answer 40

incinerate waste to produce chemicals
burn plastic produces heat energy

Question 41

how does chemical feedstock work

Answer 41

plastic used as chemical feedstock
breaks down into polymers and rebuilds